1. Field of the Invention
The present invention relates to a motor, more particularly, to a series-excited direct current (DC) motor.
2. Description of the Related Art
For a DC motor capable of rotating in forward and inverse directions, the rotating direction is changed by changing a direction of the current supplied to the exciting coil. Conventionally, the controller capable of changing the direction of the current supplied to the exciting coil is disposed outside the motor, for example, mounted on the outer surface of the motor shell, and usually comprises four contactors, so that the controller has a plurality of wires and connection points.
Therefore, the motors of the type commonly known in the related art have a large volume, are not compact in structure, and occupy a large mounting space. Moreover, the controller needs to be enclosed, and the wires and connection points thereof need to be sealed and insulated respectively. These requirements increase the cost and reduces the operating efficiency of the motors.
Additionally, due to the large number of the wires and connection points, the work load of sealing and insulating the motor is large, the operation is complex, and the power consumption is increased. Further, because the controller is disposed outside the motor, the current direction controller and wires and connection points thereof tend to be damaged, thus causing higher maintenance cost.